1. Field of the Invention
The invention relates to cannulas for study of patients during sleep and monitoring their vital signs. Specifically, the invention relates to integrated cannulas that support sensors for monitoring a patient's vital signs including temperature and respiration pressure.
2. Description of Related Art
A cannula is a thin tube inserted into a body cavity. Certain cannulas are used to insert into a patient's nostrils to provide assisted respiration to the patient. Typically, respiratory cannulas are used to deliver oxygen to a patient.
The respiration of patients has become more sophisticated and often includes the monitoring of vital signs such as temperature and respiration pressure. The monitoring of these vital signs can permit an electronic device to detect irregularities in a patient's breathing. Apnea is one such irregularity wherein the patient's breathing stops. The electronic device can “alert” medical personnel through an alarm or other signal as to the irregularity or disruption in the patient's breathing.
Sophisticated electronic monitoring devices require sensors placed at exact points in the path of the patient's respiration. A failure to place the sensor correctly or to hold it firmly in place jeopardizes the reliability of the monitoring and subsequent alarms. Further, the more sensors that are held at critical locations for monitoring vital signs, the more awkward and uncomfortable the device is for the patient.
The industry has combined sensors and cannulas. These combinations tend to be limited in the vital signs that can be monitored or cumbersome for the patient.
U.S. Pat. No. 4,686,975 to Naimon et al. describes an electronic respirable gas delivery device. The invention includes a respiration sensor where a nasal cannula is connected via tubing to a sensitive pressure transducer with an amplifier for transforming the gas flow, depending upon pressure variations at the nasal cannula prongs, into an electrical signal for diagnostic information concerning the breathing pattern. The device does not provide any means for sensing oral breathing simultaneously with nasal breathing.
U.S. Pat. No. 5,069,222 to McDonald, Jr., describes a respiration sensor set. The invention includes a respiration sensor set with a pair of spaced-apart nasal temperature sensors and one oral temperature sensor. Support means hold the two nasal sensors in a spaced-apart condition and in parallel. The oral sensor is spaced apart in an axial alignment with one of the nasal sensors. This device provides only thermal indications of breathing and requires three temperature sensors. This device does not provide for a detector for respiration pressure.
U.S. Pat. No. 6,155,986 to Brydon et al. describes an apparatus for the monitoring of oro-nasal respiration. The device includes a respiration sensor system where a nasal cannula with two prongs is connected in parallel with the tubing from a third prong placed in the proximity of a patient's mouth. At the junction of the two tubes a single common tube is connected to a sensitive pressure transducer for monitoring oro-nasal respiration. The pneumatic impedances of the oral tube and the nasal tube are arranged to be different so that the contributions of respiratory flow from each of the tubes is substantially equal. The device uses only pressure sensing of breath flow which is unreliable at shallow breathing (low flow), and displacement of the prong in proximity to the mouth is very critical in order to provide a representative monitoring of mouth breathing.
U.S. Pat. No. 6,165,133 to Rapoport et al. describes an apparatus and method for monitoring breathing patterns. The device combines a respiration sensor system where a nasal cannula with two prongs has two temperature sensors attached to the nasal prongs and a third temperature sensor attached to an extension. The extension is oriented in the proximity of the patient's mouth. The two nasal temperature sensors are either attached to the outside of the prongs or just outside the opening of each prong. The device requires three temperature sensors and the position of the nasal sensors on the outside of the prongs can easily cause them to get in contact with secretion or be subject to fluid droplets which can cause the sensing of air temperature fluctuations to fail.
Diagnostic sleep studies or “polysomnograms” typically record parameters related to a patient's breathing in order to determine if a condition known as sleep apnea is present. Standard sensors include respiratory effort belts on the chest and abdomen, snore sensors or microphones on the neck, a body position sensor, and either thermal or pressure sensors to detect oral and/or nasal airflow. Thermal airflow detects a change in temperature between warm exhaled air and cooler room air that is inhaled. Thermal airflow is a good indicator of the presence or absence of breathing, but it does not measure the volume of airflow. Thermal airflow sensors are generally either a thermistor or a thermocouple but can be any sensor capable of detecting changes in airflow temperature.
The American Academy of Sleep Medicine (“AASM”) recently revised its recommendations for sensor usage in accredited sleep labs. The AASM recommends that accredited sleep labs use a pressure transducer to detect hypopneas. Hypopneas occur when there is a greater than 50 percent reduction in breathing (as measured by volume of air exchanged) and a 10 second or greater cessation of breathing (as measured by a thermal sensor to detect apneas). This recommendation for the use of two different types of sensors has created a practical problem for polysomnographic technologists charged with preparing a patient for a sleep study and attaching the required sensors.
Both the thermal and pressure airflow sensors need to rest on the upper lip in order to sample the airflow from the patient's nasal and oral cavities. The presence of two separate sensors is often uncomfortable for the patient and difficult for the technologist to position properly.
The industry lacks an integrated cannula that provides for sensing nasal and/or oral breath temperatures and for sensing the pressure of the nasal breaths.